Storage buildings of nuclear power plants are generally constructed by a post-tensioning construction method to obtain structural reinforcement. In the post-tensioning construction method, a load is applied based on a design value of an initial tensioning amount, which is obtained by calculating a creep amount related to a concrete tensioning amount and other reasons. Therefore, since the creep amount of concrete must be obtained by an actual experiment before post-tensioning construction of the storage buildings, it is necessary to measure a precise creep amount.
A conventional creep tester for measuring the creep amount is generally designed to apply a load of about 50 tons with a hydraulic jack.
Therefore, it is necessary for the conventional creep tester to have an apparatus for applying hydraulic pressure, that is, a hydraulic pressure actuator. However, since it is impossible to achieve complete sealing due to characteristics of hydraulic pressure, the hydraulic pressure actuator requires periodic supplementation of hydraulic pressure to have a constant hydraulic pressure during operation.
As such, since the conventional creep tester using the hydraulic pressure experiences a decrease in hydraulic pressure with elapse of time, a manual operation or a separate electrical device must be performed or used for continuous supplementation of the hydraulic pressure. However, since such a manual operation or a separate electrical device is also operated based on detection of sensors in a predetermined range of hydraulic pressure, they have a problem in that a precise load cannot be continuously applied to test concrete samples.